Why is my model showing different shading on a flat area around a hole?
It looks to me like you simply have smooth shading turned on. In edit mode, in the 3d view, the toolbar on the left (in your picture it says "Add Meshes" at the top), go to the transform tab, and in the "Edit" section, look for a label called "Shading:". Under that, there should be two buttons, one says "smooth" and the other says "flat". Click the one that says "flat" and see if those dark patches go away.